Bearing calculator and error correction method

ABSTRACT

A bearing calculator provided with a geomagnetic sensor for detecting earth-geomagnetism and a control unit for calculating a geographical bearing based on detection values of the geomagnetic sensor. The control unit can execute offset error correction processing for correcting the offset error to the geomagnetic sensor based on a change in the magnetic field inside the bearing calculator. When detection values of the geomagnetic sensor enter an abnormal state, it performs said offset error correction processing when the abnormal state continues for a predetermined time, while does not perform the offset error correction processing when the abnormal state ends within a predetermined time.

CROSS-REFERENCE TO THE RELATED APPLICATIONS

This application is a divisional of application Ser. No. 12/848,831,filed on Aug. 2, 2008, which is a continuation of application Ser. No.10/599,536, filed on Jul. 30, 2007, which is a U.S. Pat. No. 7,769,539,which is a national stage of international application No.PCT/JP2005/006333, filed on Mar. 31, 2005, the entire contents of whichare incorporated herein by reference. This application also claims thebenefit of priority under 35 USC 119 to Japanese Patent Application No.2004-107771, filed on Mar. 31, 2004, the entire contents of which areincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a movable communication apparatus suchas a mobile phone provided with a geomagnetic sensor for measuring thegeographical bearing and a method for correcting the geomagnetic sensor.

BACKGROUND ART

Conventionally, there has been a demand for a device to confirm thegeographical location of a present position and provide guidance on theroute to a target position by a map. As a device satisfying such demand,car navigation systems are known (for example Patent Document 1, PatentDocument 2, and Patent Document 3).

In general, a car navigation system calculates the geographical locationof the present position by receiving and processing signals transmittedfrom a plurality of GPS (global positioning system) satellites(hereinafter described as “GPS signals”), reads out map data on thesurroundings of this present position from a database stored in astorage unit (DVD, hard disc, etc.) in the system, and displays it on adisplay. Further, a path of movement of a vehicle is calculated by usinga car speed sensor and a gyro sensor, map matching processing fordetecting a degree of coincidence between this and a road on the map iscarried out, and error of the position finding is corrected.

However, there is a demand for a user to determine his own location andlearn the route up to the target position even when he is not in avehicle. As a device satisfying such a demand, a mobile cellular phonemounting a simple map information display processing function hasappeared.

Initially, mobile cellular phones equipped with map information displayprocessing functions lacked a device for measuring the bearing,therefore a map display easily understood by the user such as a headingup display (display rotating the map so that an advancing direction wasdirected toward the top of a screen) which was generally performed in acar navigation system was difficult.

Therefore, in recent years, a mobile cellular phone equipped with a mapinformation display processing function measuring the bearing by using ageomagnetic sensor and enabling heading up display has been proposed.

Patent Document 1: Japanese Patent Publication (A) No. 2004-28837

Patent Document 2: Japanese Patent Publication (A) No.

Patent Document 3: Japanese Patent Publication (A) No. 10-197258

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

However, a geomagnetic sensor, which detects very weakearth-geomagnetism, is influenced by the magnetic fields generated by avariety of parts in a mobile cellular phone or other communicationapparatus and easily suffers from error. In particular, the recentmovable and portable cellular phones are being made smaller in size.Sufficient distance between parts is becoming harder to secure.Therefore, the error of detection of the earth-geomagnetism due to themagnetic fields generated from parts in the communication apparatus hasbecome a non-negligible level. For this reason, in a mobile cellularphone to/from which for example a memory card can be attached/detachedand further configured so that a read/Write operation is possible, thereis the problem that the results of calculation of the bearing becomedifferent between a state where the memory card is loaded and a statewhere it is not loaded.

On the other hand, among the recent movable and portable cellularphones, along with the enlargement of the display screens, many deviceshave appeared with the display unit and key input unit provided indifferent cases. This type of cellular phone is generally used in astate where the two housings are superposed over each other by foldingand the key input unit is hidden inside the cases (closed state) or astate where both of the key input unit and the display unit are exposed(open state).

This two-case type cellular phone includes a type in which the displayunit is hidden inside the cases in the closed state and a type in whichthe display unit is exposed at the outside of the cases as it is. Arepresentative example of the latter type includes a type where thesurface of the display unit and the surface of the key input unit arerotated relative to each other in an almost parallel state.

In this way, in a cellular phone of a type able to use the display unitin both of the open state and the closed state, it is desired to use themap information display processing function in both of the two states.However, when the open/closed state of cases is changed, the magneticfield surrounding the geomagnetic sensor changes, therefore there is theproblem that the results of measurement of the bearing become different.

Further, in a mobile cellular phone, due to restrictions on the size andcost, it is difficult to correct the measurement error of the bearing byusing a detection method other than a geomagnetic sensor, for example,detection of a direction of movement using a gyro sensor in a carnavigation system.

The present invention was made in consideration with such circumstancesand has as an object thereof to provide A bearing calculator able tofind a bearing with a high precision by using a geomagnetic sensor andable to correct offset due to a change in magnetic field.

Another object of the present invention is to provide an errorcorrection method enabling the correction of offset due to a change inmagnetic field.

Means for Solving the Invention

According to the present invention, there is provided a bearingcalculator provided with a geomagnetic sensor for detectingearth-geomagnetism and a control unit for calculating a geographicalbearing based on detection values of the geomagnetic sensor, wherein thecontrol unit can execute a offset error correction processing forcorrecting offset error to the geomagnetic sensor due to a change ofmagnetic field in the bearing calculator and, when detection values ofthe geomagnetic sensor become abnormal state, performs the offset errorcorrection processing if the abnormal state continues for apredetermined time, and does not perform the offset error correctionprocessing if the abnormal state ends within a predetermined time.

Further, according to the present invention, there is provided an errorcorrection method in a bearing calculator provided with a geomagneticsensor for detecting earth-geomagnetism and a control unit forcalculating a geographical bearing based on detection values of thegeomagnetic sensor, comprising an offset error correction processingstep of correcting an offset error to the geomagnetic sensor due to achange of magnetic field in the bearing calculator; an abnormal statedetection step of detecting that detection values of the geomagneticsensor become abnormal; and a judgment step of judging whether or not anabnormal state continues for a predetermined time when the abnormalstate is detected at the abnormal state detection step, said offseterror correction processing step is carried out when it is judged insaid judgment step that said abnormal state continues for apredetermined time, while said offset error correction processing stepis not carried out when it is judged that said abnormal state does notcontinue for said predetermined time.

EFFECT OF THE INVENTION

According to the present invention, the bearing is found with a highprecision by using a geomagnetic sensor, and offset due to a change inmagnetic field can be corrected.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an example of the configuration of asystem for acquiring geographical location and information of a map in amobile cellular phone according to an embodiment of the presentinvention;

FIG. 2 is a perspective view of a mobile cellular phone in an openstate;

FIG. 3 is a perspective view from one side surface of the mobilecellular phone in a closed state;

FIG. 4 is a perspective view from the other side surface of the mobilecellular phone in the closed state;

FIG. 5 is a perspective view showing a board mounted state inside aboard mounting case;

FIG. 6 is a block diagram showing an example of the configuration of amobile cellular phone according to an embodiment of the presentinvention;

FIG. 7 is a flow chart illustrating an example of GPS signal receptionprocessing in a mobile cellular phone;

FIG. 8 is a flow chart illustrating an example of position findingprocessing in a mobile cellular phone;

FIG. 9 is a diagram showing an example of map information transmittedfrom a navigation server system;

FIG. 10 is a flow chart illustrating an example of rotation processingfor a display image in a mobile cellular phone;

FIG. 11 is a diagram for explaining a method of calculation of anazimuth angle;

FIG. 12 is a flow chart illustrating a first example of processing forcalculation of the bearing in a mobile cellular phone;

FIG. 13 is a diagram showing an example of correction data;

FIG. 14 is a flow chart illustrating a second example of processing forcalculation of the bearing in a mobile cellular phone;

FIG. 15 is a flow chart illustrating a third example of processing forcalculation of the bearing in a mobile cellular phone;

FIG. 16 is a flow chart illustrating a fourth example of processing forcalculation of the bearing in a mobile cellular phone;

FIG. 17 is a flow chart illustrating a fifth example of processing forcalculation of the bearing in a mobile cellular phone;

FIG. 18 is a diagram showing an example of changes in a geomagneticsensor detection value along with time in accordance with presence of aloaded memory card;

FIG. 19 is a flow chart illustrating a sixth example of processing forcalculation of the bearing in a mobile cellular phone;

FIG. 20 is a flow chart illustrating a first example of processing forcorrection of offset error in a case where an abnormal state occurs in aearth-geomagnetism detection value;

FIG. 21 is a diagram showing an example of the abnormal state of aearth-geomagnetism detection value occurring due to influence of anexternal magnetic field;

FIG. 22 is a flow chart illustrating a second example of processing forcorrection of offset error in a mobile cellular phone;

FIG. 23 is a flow chart illustrating a third example of processing forcorrection of offset error in a mobile cellular phone;

FIG. 24 is a flow chart illustrating a first example of processing in acase where an error occurs in a earth-geomagnetism detection value dueto the influence of an external magnetic field;

FIG. 25 is a flow chart illustrating a second example of processing in acase where an error occurs in a earth-geomagnetism detection value dueto the influence of an external magnetic field;

FIG. 26 is a flow chart illustrating a third example of processing in acase where an error occurs in a earth-geomagnetism detection value dueto the influence of an external magnetic field;

FIG. 27 is a flow chart illustrating a fourth example of processing in acase where an error occurs in a earth-geomagnetism detection value dueto the influence of an external magnetic field;

FIG. 28 is a flow chart illustrating a fifth example of processing in acase where an error occurs in a earth-geomagnetism detection value dueto the influence of an external magnetic field;

FIG. 29 is a flow chart illustrating a sixth example of processing in acase where an error occurs in a earth-geomagnetism detection value dueto the influence of an external magnetic field;

FIG. 30 is a flow chart illustrating a seventh example of processing ina case where an error occurs in a earth-geomagnetism detection value dueto the influence of an external magnetic field;

FIG. 31 is a flow chart illustrating an eighth example of processing ina case where an error occurs in a earth-geomagnetism detection value dueto the influence of an external magnetic field; and

FIG. 32 is a flow chart illustrating an example of processing forregistering a precision drop area in a storage unit in the processingshown in FIG. 28 to FIG. 31.

DESCRIPTION OF NOTATIONS

2 . . . first housing, 3 . . . second housing, 4 . . . mobile mechanism,21 . . . display panel, 100 . . . mobile cellular phone, 200 . . . GPSsatellite, 300 . . . base station, 401 . . . GPS server system, 402 . .. navigation server system, 150 . . . wireless communication unit, 151 .. . GPS signal receiver, 152 . . . storage unit, 153 . . . open/closejudgment unit, 154 . . . key input unit, 155 . . . audio processingunit, 157 . . . image capture unit, 158 . . . geomagnetic sensor, 159 .. . memory card unit, 160 . . . control unit.

BEST MODE FOR WORKING THE INVENTION

Below, an embodiment of a case where the present invention is applied toa multi-function type movable and portable cellular phone having a mapinformation display processing function and image capturing function andable to display map information considering the bearing (hereinafterreferred to as a “mobile cellular phone”) will be explained withreference to the drawings.

FIG. 1 is a block diagram showing an example of the configuration of asystem for acquiring a geographical location and map information in acellular phone 100 according to an embodiment of the present invention.

The cellular phone 100 receives GPS signals transmitted from three ormore GPS use satellites 200 circling the globe on known orbits. Then,the cellular phone 100 transmits the information concerning the receivedGPS signals from a base station 300 through a communication network to aGPS server system 401, as one example of the position finding means ofthe present invention, and acquires the location information of thepresent position from the GPS server system 401.

Further, the cellular phone 100 transmits the location information ofthe present position acquired from the GPS server system 401 from thebase station 300 through the communication network to the navigationserver system 402, as one example of the position finding means of thepresent invention, and acquires the map information on the surroundingsof the present position from the navigation server system 402.

The GPS server system 401, as one example of the position finding meansof the present invention, calculates the geographical location (forexample latitude and longitude) of the cellular phone 100 based on theGPS signals sent from the cellular phone 100 via the communicationnetwork and transmits the calculated location information through thecommunication network and the base station 300 to the cellular phone100.

The navigation server system 402, as one example of the position findingmeans of the present invention, retrieves the map information on thesurroundings of the cellular phone 100 from a not shown database basedon the map information sent from the cellular phone 100 via thecommunication network and transmits the retrieved map informationthrough the communication network and the base station 300 to thecellular phone 100.

FIG. 2 to FIG. 4 are diagrams showing an example of the appearance ofthe cellular phone 100.

FIG. 2 is a perspective view of the cellular phone 100 in the openstate, FIG. 3 is a perspective view from one side surface of thecellular phone 100 in the closed state, and FIG. 4 is a perspective viewfrom another side surface of the cellular phone 100 in the closed state.

In the cellular phone 100, a first housing (upper housing) 2 and asecond housing (lower housing) 3 are connected via a movable mechanismunit 4 so that they can freely open/close and/or freely rotate.

The movable mechanism unit 4 is configured so that it can relativelyrotate the first housing 2 and the second housing 3 and/or open/closethem about a predetermined rotation axis.

In the first housing 2, a first surface 2 a exposed irrespective of theoperation state (open state, closed state) of the movable mechanism unit4 is provided with a display panel 21 configured by for example an LCD(liquid crystal display) panel or organic EL (electroluminescent)display panel. At the left side corner in FIG. 2 of this display panel21, a speaker 22 is built in.

The display panel 21 is included in a display unit 155 explained later.The speaker 22 is included in an audio processing unit 156 explainedlater.

The second housing 3 is configured by superimposing a board mountinghousing 31 having a board mounted therein and a lid side housing 32forming the lid of the board mounting housing 31 on each other.

On an outer flat surface 31 a of the board mounting housing 31 of thesecond housing 3, that is, the surface 31 a facing one surface of thefirst housing 2 at the time of the closed state, operation keys 311including tenkey buttons 311 a, cursor buttons 311 b, and an enter key311 c are arranged. At the right side corner in FIG. 2 of the operationkeys 311, a microphone 312 is built in.

The operation keys 311 are included in a key input unit 154 explainedlater. The microphone 312 is included in the audio processing unit 156explained later.

On an outer flat surface 32 a exposed irrespective of the open state orclosed state of the lid side housing 32 of the second housing 3, asshown in FIG. 4, an optical system 34 a of a camera module 34 isarranged.

On the outer flat surface 32 a of the lid side housing 32 of the secondhousing 3, a light emitting window 321 for emitting a flash by abuilt-in flash lamp to the outside and a light emitting window 322 foremitting white light for assisting image capture at the time of taking aphotograph etc. are arranged.

The camera module 34 is included in an image capturing unit 157explained later.

Camera module use tact switches 35 are arranged at one side of thesecond housing 3, while a memory card use slot 33 for inserting a memorycard is formed at the other side of the second housing 3.

FIG. 5 is a perspective view showing a board mounted state in an inside31 b of the board mounting housing 31.

In the inside 31 b of the board mounting housing 31, a main board 37 ismounted over its bottom surface.

At a location facing the memory card use slot 33 on the main board 37, amemory card unit 159 to which a detachable memory card may be attachedis mounted.

At the substantial center position of the main board 37 adjacent to thismemory card unit 159, a geomagnetic sensor 158 is mounted.

FIG. 6 is a block diagram showing a illustrative example of theconfiguration of the cellular phone 100 according to the embodiment ofthe present invention.

The cellular phone 100 has a wireless communication unit 150, GPS signalreceiver 151, storage unit 152, open/close judgment unit 153, key inputunit 154, display unit 155, audio input/output unit 156, image capturingunit 157, geomagnetic sensor 158, memory card unit 159, and signalprocessing/control unit 160.

The wireless communication unit 150 is an embodiment of the wirelesscommunicating means of the present invention.

The GPS signal receiver 151 is an embodiment of the GPS signal receivingmeans of the present invention.

The GPS signal receiver 151 and the wireless communication unit 150 arean embodiment of the location information acquiring means of the presentinvention.

The open/close judgment unit 153 is an embodiment of the operation statejudging means of the present invention.

The display unit 155 is an embodiment of the displaying means of thepresent invention.

The geomagnetic sensor 158 is an embodiment of the geomagnetic sensor ofthe present invention.

The memory card unit 159 is an embodiment of the storage medium mountingmeans of the present invention.

The signal processing/control unit 160 is an embodiment of the signalprocessing/controlling means of the present invention.

The wireless communication unit 150 performs processing concerningwireless communication with the base station 150 in cooperation with thesignal processing/control unit 160. For example, it appliespredetermined modulation processing to the transmission data output fromthe signal processing/control unit 160 to convert it to a wirelesssignal and transmits the same from a first antenna AT1. Further, thewireless communication unit 150 applies predetermined demodulationprocessing to the wireless signal received at the first antenna AT1 toreproduce the reception data and outputs the same to the signalprocessing/control unit 160.

The wireless communication unit 150 also performs processing forreceiving a reference signal for position finding transmitted from thebase station 300 serving as the location information acquiring means.

The GPS signal receiver 151, in cooperation with the signalprocessing/control unit 160, receives the GPS signal transmitted fromthe GPS use satellites 20 via a second antenna AT2 and applies signalprocessing such as amplification, noise elimination, and modulation toacquire the information required for calculating the geographicallocation of the cellular phone 100 in the GPS server system 401.

The storage unit 152, in cooperation with the signal processing/controlunit 160, stores a program to be executed in the signalprocessing/control unit 160, constant data used in the processing forthe signal processing/control unit 160, and variable data, imagecapturing image data, etc. which must be temporarily stored.

The open/close judgment unit 153, in cooperation with the signalprocessing/control unit 160, judges which of the open state or theclosed state explained above is the state of rotation of the firsthousing 2 and the second housing 3 by the movable mechanism unit 4. Forexample, the open/close judgment unit 153 includes a detector such as aswitch for detecting the closed state where the first housing 2 and thesecond housing 3 are superimposed so as to distinguish between theclosed state and the state other than that.

The key input unit 154, in cooperation with the signalprocessing/control unit 160, generates a signal in accordance with anyinput operation such as depression of a key carried out with respect tothe operation keys 311 and the camera module use tact switches 35 andoutputs the same to the signal processing/control unit 160.

The display unit 155 makes the display panel 21 display an image inaccordance with the image data generated in the signalprocessing/control unit 160 in cooperation with the signalprocessing/control unit 160.

The audio processing unit 156, in cooperation with the signalprocessing/control unit 160, converts an input audio to an electricaudio signal at the microphone 312, applies processing such asamplification, analog-digital conversion, and encoding to this, andoutputs the audio data as the result of the processing to the signalprocessing/control unit 160. Further, the audio processing unit 156applies signal processing such as decoding, digital/analog conversion,and amplification to the audio data input from the signalprocessing/control unit 160 to generate an audio signal and convertsthis to audio at the speaker 22.

The image capturing unit 157, in cooperation with the signalprocessing/control unit 160, captures the image incident at the opticalsystem 34 a to generate image data such as a still image and movingimage and outputs the same to the signal processing/control unit 160.The image capturing unit 157, under the control of the signalprocessing/control unit 160, operates the flash lamp at the time of theimage capture to emit a flash from the light emitting window 321.

The geomagnetic sensor 158 detects the earth-geomagnetism used for thecalculation of the bearing. For example, as shown in FIG. 5, thegeomagnetic sensor 158 detects the earth-geomagnetism in each axialdirection at a fixed location on the main board 37 with reference to aCartesian coordinate system set on the main board 37. For the detectionof the earth-geomagnetism, use is made of various methods such as amethod utilizing excitation of a coil, a method utilizing the Halleffect, and a method utilizing a magnetoresistance element.

In the present embodiment, as an example, it is assumed that thegeomagnetic sensor 158 mounts an analog-digital converter and outputsanalog signals of the detected earth-geomagnetism as 8-bit digitalsignals, that is, integer values of from “0” to “255”.

The signal processing/control unit 160 has a computer for executingprocessing based on a program stored in the storage unit 152 andperforms various processing concerning the overall operation of thecellular phone 100.

For example, as processing concerning the phone function, the signalprocessing/control unit 160 performs processing for controlling thesequence of calling and reception via the wireless communication unit150 in accordance with a key input operation in the key input unit 154and processing for transmitting/receiving the audio data input/output atthe audio processing unit 156 via the wireless communication unit 150.

As processing concerning the data communication function, the signalprocessing/control unit 160 operates the wireless communication unit 150in response to a key input operation in the key input unit 154, performsthe communication with a predetermined mail server system, and performsa processing for transferring the data such as electronic mail.

As the processing concerning the image capturing function, the signalprocessing/control unit 160 performs processing for making the imagecapturing unit 157 execute processing to capture a still image andmoving image in response to a key input operation in the key input unit154 and processing for applying image processing such as compression andencoding to the data of the captured image and storing the result in thestorage unit 152 etc. At the time of the capture of a still image, thesignal processing/control unit 160 also performs processing foroperating the flash lamp at a suitable timing.

The signal processing/control unit 160, as processing concerning the mapinformation display processing function, performs processing forcalculating the geographical bearing based on the detection value of thegeomagnetic sensor 158, processing for transmitting information of theGPS signals received at the GPS signal receiver 151 to the GPS serversystem 401 and acquiring the location information of the presentposition, processing for transmitting this location information to thenavigation server system 402 and acquiring the information of a map onthe surroundings of the present position, processing for calculating thepresent position based on a position finding signal from the basestation 300 and the result of calculation of the bearing, processing forcontrolling the orientation of the map on the display screen of thedisplay unit 155 in accordance with the result of calculation of thebearing (heading up display processing), etc.

The signal processing/control unit 160, in order to deal with the factthat the orientation of the display panel 21 with respect to the userdiffers by 180 degrees between the open state and the closed state ofthe first housing 2 and the second housing 3, performs processing forrotating the displayed image of the display unit 155 in accordance withthe judgment result of the open/close judgment unit 153.

The operation of the cellular phone 100 having the configurationexplained above will be explained next focusing on the map displayprocessing function according to the present invention.

First, the processing for reception of the GPS signal performedprincipally by the signal processing/control unit 160 when the power ofthe cellular phone 100 is turned on will be explained.

FIG. 7 is a flow chart illustrating an example of the GPS signalreception processing in the cellular phone 100.

The signal processing/control unit 160 controls the GPS signal receiver151 at a constant cycle of for example an interval of 2 seconds (ST102,ST104) and performs a scan for receiving a GPS signal from a GPSsatellite. When the result of the scan is that the GPS signal can bereceived, the signal processing/control unit 160 stores the received GPSsignal in the storage unit 152 (ST106). Such a scan for a GPS signal andthe storage of the information are repeated for all GPS satellites fromwhich data can be received (ST108, ST104, ST106). When the scan iscarried out for all GPS satellites, the signal processing/control unit160 waits until the next GPS signal reception timing, then performs theprocessing for steps ST104 to 108 again.

Next, the position finding processing will be explained.

FIG. 8 is a flow chart illustrating an example of the position findingprocessing in the cellular phone 100.

The signal processing/control unit 160, when a start of the positionfinding processing is selected by for example a key input operation inthe key input unit 154 (ST122), performs the processing for transmittingthe information obtained by the above GPS reception processing from thewireless communication unit 150 via the base station 300 and thecommunication network to the GPS server system 401 (ST124).

The GPS server system 401, when receiving the GPS information from thecellular phone 100, calculates the location of the present position (forexample latitude and longitude) of the cellular phone 100 based on thisreceived GPS information and transmits the result of the calculationfrom the communication network through the base station 300 to thecellular phone 100.

The signal processing/control unit 160 receives the location informationtransmitted from the GPS server system 401 and stores the same in thestorage unit 152 (ST126).

Next, the signal processing/control unit 160 accesses the navigationserver system 402 from the wireless communication unit 150 via the basestation 300 and the communication network (ST128) and transmits theacquired location information to the navigation server system 402(ST130).

The navigation server system 402, when receiving the locationinformation from the cellular phone 100, retrieves the map informationon the surroundings of the present position of the cellular phone 100specified by this location information from the database and transmitsthe retrieved map information from the communication network via thebase station 300 to the cellular phone 100.

The signal processing/control unit 160 receives the map informationtransmitted from the navigation server system 402 and stores the same inthe storage unit 152 (ST132).

FIG. 9 is a diagram showing an example of the map informationtransmitted from the navigation server system 402.

In the present embodiment, as an example, it is assumed that inherentidentification numbers are assigned to the map information. Thenavigation server system 402, based on the identification numbers,manages the map data for each predetermined size (for example 1 kmsquare) and, when transmitting the map information to the cellular phone100, attaches these identification numbers to the data of the map fortransmission. In the example of FIG. 9, the map of the surroundings ofthe present position has an identification number MP0, and the mapsaround that in the four directions have the identification numbers MP1to MP4.

The signal processing/control unit 160, when receiving such mapinformation, generates the image data of the map on the surroundings ofthe present position based on the acquired map information and displaysthe map on the display panel 21 of the display unit 155 (ST134).

The region of the map displayed on the display panel 21 is a regionsmaller than the 1 km square map acquired from the navigation serversystem 402 (for example 200 m×300 m).

As the display method of the map, it is possible to select either of forexample north up display (the display of turning the north of the maptoward the top of the screen) and heading up display (the display ofturning the advancing direction on the map toward the top of thescreen).

When a north up display is selected by the key operation of the keyinput unit 154, the signal processing/control unit 160 fixes the northdirection of the map at the upward direction of the display screen anddisplays it on the display unit 155.

When a heading up display is selected by the key operation of the keyinput unit 154, the signal processing/control unit 160 performs theprocessing for controlling the orientation of the map on the displayscreen in accordance with the bearing found by the processing forcalculation of the bearing explained later. For example, when adirection A going from one end at which the microphone 312 of the secondhousing 3 is arranged toward the other end having a connection part (seeFIG. 2) is determined as the advancing direction of the cellular phone100, the orientation of the map on the display screen is controlled sothat the bearing of this advancing direction becomes upward on thedisplay screen.

“Upward on the display screen” explained here is the case seen from theviewpoint of the user holding the second housing 3 and utilizing thecellular phone 100. When the open/closed state of the housings 2 and 3is changed, “upward on the display screen” changes in accordance withthis. Namely, when the housings 2 and 3 are in the open state, thespeaker 22 side in the first housing 2 becomes the top of the displayscreen, while when the housings 2 and 3 are in the closed state, theconnection part side of the first housing 2 becomes the top of thedisplay screen.

The signal processing/control unit 160, as will be explained later,performs processing for rotating the image on the display screen inaccordance with the open/closed state of the housings 2 and 3 anddisplays the image in a suitable orientation with respect to the user.

When the display of the map is started as explained above, the signalprocessing/control unit 160 repeats the processing for step ST138 andthe following steps explained next during the period until the end ofthe position finding processing is selected by the key operation of thekey input unit 154 (ST136).

First, the signal processing/control unit 160 makes the wirelesscommunication unit 150 receive reference signals for position findingtransmitted from the plurality of (for example three or more) basestations 300 in the surroundings of the cellular phone 100 andcalculates the location of the present position based on the receivedsignals (ST138). Then, the signal processing/control unit 160 judges forthe presence of any movement of the cellular phone 100 from the resultsof calculation of the present position (ST140) and, when judging thatthe cellular phone 100 does not move, subsequently performs thecalculation of the present position based on the reference signals fromthe base stations 300 (ST138).

Where judging at step ST140 that the cellular phone 100 moves, thesignal processing/control unit 160 judges whether or not the point beingmoved to exists in a region at an end of the map which is acquired atpresent (ST142). For example, when the part of the map to be displayedon the display unit is not included in the map acquired at present, butis included in a map adjacent to this, it is judged that the presentposition exists in the region at an end of the map.

When judging that the present position exists at an end region, thesignal processing/control unit 160 requests the map adjacent to this endregion from the navigation server system 146 by the wirelesscommunication unit 150 (ST146). For example, it transmits theidentification number of the map being acquired at present and theinformation indicating to which bearing among east, west, south, andnorth is the present position adjacent to with respect to this map tothe navigation server system 146.

The navigation server system 146 detects the map in accordance with theinformation sent from the cellular phone 100 from the database andtransmits the same to the cellular phone 100.

The signal processing/control unit 160 receives the map informationtransmitted from the navigation server system 402, stores the same inthe storage unit 152 (ST132), and displays the map in accordance withthe map information on the display unit 155 (ST134). Thereafter, itrepeats the processing for step ST138 and the following steps.

Further, when judging that the present position does not exist at theend region, the signal processing/control unit 160 performs processingfor moving the display region of the map so that for example the presentposition of the cellular phone 100 becomes the center of the map beingdisplayed in accordance with the results of calculation of the presentposition. Thereafter, the signal processing/control unit 160 repeats theprocessing for step ST138 and the following steps.

Next, as an example of an “event” for the cellular phone 100, theprocessing for rotation of the display image in accordance with when theopen/closed state of the cases changes will be explained.

FIG. 10 is a flowchart illustrating an example of the processing forrotation of the display image in the cellular phone 100.

The signal processing/control unit 160 constantly monitors theopen/closed state judged in the open/close judgment unit 153 during aperiod when the power of the cellular phone 100 is ON (ST162). When theopen/close judgment unit 153 judges that the cases are not in the closedstate (that is, they are in the open state), the signalprocessing/control unit 160 displays the image on the display panel 21with an orientation so that the speaker 22 side in the first housing 2becomes the top of the image (ST166).

When this display in the open state is the ordinary display, in the casewhere the closed state is judged by the open/close judgment unit 153,the signal processing/control unit 160 rotates the image in the ordinarydisplay by 180 degrees and displays it on the display panel 21 (ST164).Namely, it displays the image on the display panel 21 with anorientation so that the connection part side of the first housing 2becomes the top of the image.

According to such rotation processing for the display image,irrespective of the open/closed state of the housings 2 and 3, the imagecan be always displayed on the display unit 155 with an orientation easyfor the user to view.

Processing for Calculation of Bearing

First, the method of calculation of the bearing will be explained inbrief with reference to FIG. 11, then some examples of the processingfor calculation of the bearing in the signal processing/control unit 160will be explained with reference to FIG. 12 to FIG. 19.

FIG. 11 is a diagram for explaining the method of calculation of theazimuth angle.

In FIG. 11, a Cartesian coordinate system having the coordinate axes Hx,Hy, and Hz is the standard coordinate system set on the horizon plane.The coordinate axes Hx and Hy are coordinate axes parallel to thehorizon plane, and the coordinate axis Hz is the coordinate axisoriented in a direction vertical to the horizon plane.

The azimuth angle θ is an angle formed by an image Zxy obtained byorthogonal projection, onto the horizon plane, of a vector in areference direction RD (for example the direction A in FIG. 2) of theearth-geomagnetism detection set for the geomagnetic sensor 158 providedon the main board 37 of the second housing 3 and the coordinate axis Hx.An inclination angle φ is the angle formed by this image Zxy and thevector in the reference direction A. Further, a twist angle η is theangle formed by rotating the cellular phone 100 around a rotation axiscomprised of the vector of the reference direction A.

When all of the azimuth angle θ, the inclination angle φ, and the twistangle η are zero, the coordinate system of the earth-geomagnetismdetection set on the main board 37 of the second housing 3 coincideswith the coordinate system of the coordinate axes Hx, Hy, and Hz shownin FIG. 11.

When the earth-geomagnetism detection value corresponding to thecoordinate axis Hx according to the geomagnetic sensor 158 is α, theearth-geomagnetism detection value corresponding to the coordinate axisHy is β, and the earth-geomagnetism detection value corresponding to thecoordinate axis Hz is γ, a tangent tan θ of the azimuth angle θ shown inFIG. 11 is represented by the following equation. φ is the inclinationangle of the display panel 21.(Equation 1)tan θ=β/(γ·sin φ−α·cos φ)  (1)

In equation (1), the twist angle η is set at zero.

The signal processing/control unit 160 calculates the azimuth angle inaccordance with the detection values of earth-geomagnetism in threedirections obtained from the geomagnetic sensor 158 by using therelationship shown in Equation (1).

The signal processing/control unit 160 considers also the inclinationangle φ of the display panel 21 with respect to the horizon plane in thecalculation of the bearing explained above.

The user can view the image of the display panel 21 by a comfortableposture when inclining the display panel 21 with an angle of for exampleabout 45 degrees. Therefore, the signal processing/control unit 160calculates the bearing according to Equation (1) by using theinclination angle φ when the inclination angle φ of the display panel 21with respect to the horizon plane becomes for example preferably 45degrees.

When the inclination angle φ of the geomagnetic sensor 158 with respectto the horizon plane is different between the open state and the closedstate of the housings 2 and 3, the signal processing/control unit 160may calculate the azimuth angles of these states by considering thedifference of this inclination angle. For example, in contrast to whenthe first housing 2 and the second housing 3 are superimposed almostparallel in the closed state, assume that two housings are connected sothat the first housing 2 and the second housing 3 are relativelyinclined in the open state. In this case, when the user tries tomaintain the direction of the line of sight constant with respect to thedisplay panel 21 by both operation styles, the inclination of the secondhousing 3 with respect to the horizon plane is different between theopen state and the closed state. The difference of inclination of thesecond housing 3 means that the inclination of the reference direction Awith respect to the horizon plane is different between the open andclosed states. Therefore, the signal processing/control unit 160performs the calculation of the bearing by using the inclination angle γof a predetermined angle in accordance with the result of judgment ofthe open/close judgment unit 153. This inclination angle γ is an anglepreviously set so as to become constant in both of the open state andthe closed state when the inclination angle φ of the display panel 21with respect to the horizon plane is for example preferably 45 degrees.

The information of the inclination angle φ is previously stored in thestorage unit 152 as for example a data table. When detecting thebearing, the signal processing/control unit 160 reads out theinformation of the inclination angle φ linked with the results ofjudgment of the open/close judgment unit 153 from the data table in thestorage unit 152 and calculates the bearing by using the information ofthis inclination angle φ.

Processing for Calculation of Bearing

FIG. 12 is a flow chart illustrating an example of the processing forcalculation of the bearing in the cellular phone 100.

When the start of the position finding processing is selected by the keyinput operation etc. at the key input unit 154, the signalprocessing/control unit 160 activates the geomagnetic sensor 158 andacquires the information of the bearing (ST202), then checks whether apredetermined event (phenomenon) has occurred or end the routine(ST204).

The “predetermined event” here means an event causing a change in thedetection value of the geomagnetic sensor 158 in the circuit andprocessing system in the cellular phone 100 when displaying informationof the bearing (map of heading up display or compass indicating thebearing) on the display unit 155. This predetermined event includes anevent of operating the wireless communication unit 150 in for example acase where the map information is acquired from the navigation serversystem 402 at step ST146 of FIG. 8 and a case where call receptionprocessing and mail reception processing are carried out. Thepredetermined event may include an event changing a display luminance onthe display unit 155 in accordance with the key input operation, achange of the information of the bearing, updating of the display of themap etc., an event of operating the audio processing unit 156 andoutputting audio from the speaker, and so on. As the predeterminedevent, where the display unit 155 has an LCD panel, for example an eventof turning on/off the light source serving as the LCD back light orchanging the strength of light emission of the light source may beincluded.

When the occurrence of such a predetermined event is detected, thesignal processing/control unit 160 reads out the correction data of thepreviously prepared earth-geomagnetism detection values from the storageunit 152 corresponding to the detected event and changes the correctiondata in use at present.

FIG. 13 is a diagram showing an example of the correction data.

In the example of FIG. 13, the correction data is comprised of threecorrection values corresponding to the X-axis, Y-axis, and Z-axisdetection values of the geomagnetic sensor 158. For example, whenperforming the communication processing for operating the wirelesscommunication unit 150, the signal processing/control unit 160 reads outthe “−1”, “0”, and “−1” correction values corresponding to the X-axis,Y-axis, and Z-axis earth-geomagnetism detection values from the storageunit 152.

The storage unit 152 stores for example such correction datacorresponding to a plurality of events. Each correction value of thecorrection data is determined by previously measuring the amounts offluctuation of the earth-geomagnetism detection value in the case whereeach event occurs and the case where the event does not occur.

When detecting the occurrence of a plurality of events at step ST204,the signal processing/control unit 160 adds the correction values of thecorrection data corresponding to the detected events to theearth-geomagnetism detection values in three directions. For example, inthe example of FIG. 13, where both of communication processing and audiooutput processing occur, when the detection value of the geomagneticsensor is ±255, the X-axis correction value becomes “−1”+“−1”=“−2”, theY-axis correction value becomes “0”+“0”=“0”, and the Z-axis correctionvalue becomes “−1”+“0”=“−1”.

Further, when the end of a certain event is detected at step ST204, thesignal processing/control unit 160 subtracts the correction values ofthe correction data corresponding to the ended event from the presentvalues. For example, when the X-axis, Y-axis, and Z-axis correctionvalues at present are the states of “−2”, “−1”, and “1” and thecommunication processing shown in FIG. 13 ends, the X-axis correctionvalue is changed to “−2”−“−1”=“−1”, the Y-axis correction value ischanged to “−1”−“0”=“−1”, and the Z-axis correction value is changed to“1”−“−1”=“2”.

The signal processing/control unit 160 corrects the detection values ofthe geomagnetic sensor 158 based on the correction data read out fromthe storage unit 152 (ST208). Namely, it adds the correspondingcorrection values of the correction data to the detection values inthree directions of the geomagnetic sensor. Then, by using theearth-geomagnetism detection values after this correction, it calculatesthe bearing by the above method of calculation (ST210).

The signal processing/control unit 160 repeats the processing for stepsST204 to ST210 explained above during a period where the positionfinding processing is executed (ST212).

As described above, according to the first example of the processing forcalculation of the bearing shown in FIG. 12, when displaying theinformation of the bearing on the display unit 155, the occurrence of apredetermined event (including an end of an event) changing the magneticfield inside the cellular phone 100 is monitored by the signalprocessing/control unit 160. When the occurrence of a predeterminedevent is detected, the information of the bearing is corrected.

Accordingly, even when the detection values of the geomagnetic sensor158 change due to the occurrence of an event, and the precision of theinformation of the bearing displayed on the display unit 155 is lowered,by detecting the occurrence of the event and correcting the informationof the bearing, the precision of the information of the bearing can berestored.

Further, the correction data previously determined for each event andstored in the storage unit 152 is used for correction of the informationof the bearing, therefore the information of the bearing can becorrected with a good precision for each occurring event.

FIG. 14 is a flow chart illustrating a further example of the processingfor calculation of the bearing in the cellular phone 100.

The difference of FIG. 14 from FIG. 12 explained above resides in thepoint that during the period from detecting the occurrence of apredetermined event to the computation for correction of the informationof the bearing and the display of the information of the bearing of theresult of the computation on the display unit 155, the fact that theprecision of the information of the bearing displayed on the displayunit 155 is low is displayed on the display unit 155

Namely, when detecting the occurrence of a predetermined event at stepST204, the signal processing/control unit 160 displays the fact that theprecision of the information of the bearing displayed on the displayunit 155 is low on the display unit 155 (ST214). For example, whendisplaying an image of a compass representing the bearing, it ispossible to display movement of this compass swinging leftward andrightward so as to indicate that the precision of the information of thebearing is low. Further, it is possible to change the shape, color, andsize of the image of the compass or display another image indicatingthat the precision of the bearing is low.

The signal processing/control unit 160 displays information indicatingthe drop of precision of the bearing on the display unit 155 during achange of the correction values (ST206), correction of the magneticdetection values (ST208), and calculation of the bearing (ST210). Then,when displaying the information of the bearing after correction on thedisplay unit 155, when the precision of the bearing is restored (ST211),this restoration is displayed on the display unit 155 (ST216).

For example, when displaying a drop of the precision of the bearing bymovement swinging the image of the compass rightward and leftward, it ispossible to suspend this rightward and leftward swinging to indicaterestoration of the precision of the bearing. When displaying a drop ofthe precision of the bearing by changing the shape, color, and size ofthe image of compass, it is possible to return this to the originalstate to indicate the restoration of the precision. Alternatively, it ispossible to display another image indicating the restoration of theprecision of the information of the bearing.

As described above, according to the second example of the processingfor calculation of the bearing shown in FIG. 14, when the correctionvalues of the earth-geomagnetism detection values change due to theoccurrence of a predetermined event (including the end of an event),during the period of recalculating the bearing by new correction valuesand displaying the results on the display unit 155, the fact that theprecision of the information of the bearing being displayed is low canbe notified to the user. Due to this, the user becomes able to correctlygrasp whether or not the precision of the information of the displayedbearing is low.

FIG. 15 is a flow chart illustrating an example of the processing forcalculation of the bearing in the cellular phone 100.

In the processing for calculation of the bearing for the example of FIG.12 and FIG. 14 explained above, the change of the earth-geomagnetismdetection values occurring due to the occurrence of an event in terms ofinternal processing was corrected, but in the example of FIG. 15explained next, the change of the earth-geomagnetism detection values inaccordance with the open/closed state of the housings 2 and 3 iscorrected.

The cellular phone 100 includes for example magnets used in the speaker22 and other parts generating a static magnetic field different from thedynamic magnetic field generated for each event by the internalprocessing as explained above. Such a static magnetic field becomes acause of constant error (offset error) of the earth-geomagnetismdetection values and is corrected by the processing for correction ofoffset error explained later. However, when the open/closed state of thehousings 2 and 3 is changed, the positional relationship of these staticmagnetic field generation sources changes, therefore the offset errorchanges in accordance with this.

Therefore, in the processing for calculation of the bearing for thethird example, in order to reduce the drop of precision of the bearingcalculation value due to the change of such offset error, the correctionvalue of the offset error obtained by the processing for correction ofoffset error is separately held as an event for each of the open stateand closed state. Then, where the open/closed state of the housings 2and 3 changes, the correction values used in the correction of theoffset error are changed matching with this.

When the start of the position finding processing is selected by the keyinput operation etc. at the key input unit 154, the signalprocessing/control unit 160 activates the geomagnetic sensor 158 andacquires the information of the bearing (ST302), then checks thejudgment result of the open/close judgment unit 153 (ST304). When it isjudged at the open/close judgment unit 153 that the housings 2 and 3 arein the open state, the signal processing/control unit 160 reads out theoffset error correction data of the open state held in for example a notshown register in the signal processing/control unit 160 (ST306) andcorrects the detection values of the geomagnetic sensor 158 based onthis (ST307). Further, when it is judged in the open/close judgment unit153 that the housings 2 and 3 are in the closed state, the signalprocessing/control unit 160 reads out the offset error correction dataof the closed state held in a not shown register in the signalprocessing/control unit 160 (ST308) and corrects the detection values ofthe geomagnetic sensor 158 based on this (ST309).

Note that the offset error correction data is comprised by for examplethree correction values corresponding to the earth-geomagnetismdetection values in the three directions as shown in FIG. 13. Thesecorrection values are frequently acquired at the time of the start ofthe position finding processing or during the execution thereof by theprocessing for correction of offset error explained later and writteninto the predetermined register of the signal processing/control unit160 provided for each of the open and closed states. The offset errorcorrection data stored in the register is rewritten whenever theprocessing for correction of offset error is executed and new correctionvalues are acquired.

When correcting the detection values of the geomagnetic sensor 158, thesignal processing/control unit 160 calculates the bearing by using theearth-geomagnetism detection values after this correction (ST312).

Then, the signal processing/control unit 160 acquires the judgmentresult of the open/close judgment unit 153 again and checks whether ornot the open/closed state changes (ST314).

When detecting a change from the closed state to the open state, thesignal processing/control unit 160 returns to step ST306 where it readsout the offset error correction data in the open state and repeats thecorrection of the earth-geomagnetism detection values and thecalculation of the bearing by using this (ST307, ST312). When detectinga change from the open state to the closed state, the signalprocessing/control unit 160 returns to step ST308 where it reads out theoffset error correction data in the closed state and repeats thecorrection of the earth-geomagnetism detection values and thecalculation of the bearing by using this (ST309, ST312).

When there is no change of the open/closed state, the signalprocessing/control unit 160 confirms whether or not the end of theposition finding processing is selected (ST316). When the positionfinding processing continues, the signal processing/control unit 160repeats the correction of the earth-geomagnetism detection values andthe calculation of the bearing by using the offset error correction datain use at present (ST307/309, ST312).

When the end of the position finding processing is selected, the signalprocessing/control unit 160 stores the offset error correction data ofthe open state and the closed state held in the register in the storageunit 152 (ST318). Due to this, when the position finding processing iscarried out the next time, it becomes possible to smoothly calculate thebearing by using the offset error correction data stored in the storageunit 152.

As described above, according to the example of the processing forcalculation of the bearing shown in FIG. 15, when displaying theinformation of the bearing on the display unit 155, the change of thejudgment result in the open/close judgment unit 153 is monitored, andwhen a change is detected, the information of the bearing displayed onthe display unit 155 is corrected in accordance with the state after thechange (open state or closed state). Namely, when a change is detected,the predetermined correction corresponding to the state after the changeis carried out on the detection values of the geomagnetic sensor 159,and the bearing is calculated based on these earth-geomagnetismdetection values after the correction.

Accordingly, in the cellular phone 100 structured so that the display ofthe information of the bearing by the display unit 155 is possible inboth of the open state and the closed state, even in the case where thedetection values of the geomagnetic sensor 158 change along with theoccurrence of an event such as a change of this open/closed state, andthe precision of the information of the bearing being displayed islowered, by detecting the change of the judgment result in theopen/close judgment unit 153 and correcting the information of thebearing, the precision of the information of the bearing can berestored.

Further, the offset error correction data of the open state and theclosed state are separately held in a predetermined register of thesignal processing/control unit 160, and the correction of theinformation of the bearing is carried out by using the suitable offseterror correction data in accordance with the open/closed state,therefore the information of the bearing can be corrected with a highprecision in state.

Note that, in the detection of the change of the open/closed state atstep ST314, after detecting the change of the open/closed state based onthe judgment result of the open/close judgment unit 153, by using thefact that the open or closed state after this change continues for apredetermined time, it may be finally judged that a change from the openstate to the closed state or a change from the closed state to the openstate occurs. Due to this, when the user unintentionally moves themovable mechanism unit 4 and the change of the open/closed state isinstantaneously detected, erroneous change of the offset errorcorrection data can be prevented.

FIG. 16 is a flow chart illustrating an example of the processing forcalculation of the bearing in the cellular phone 100.

The difference of FIG. 16 from FIG. 15 explained above resides in thepoint that during the period from the detection of the event of a changeof the open/closed state in the open/close judgment unit 153 to therecalculation of the bearing and the display of the recalculatedinformation of the bearing on the display unit 155, the fact that theprecision of the information of the bearing displayed on the displayunit 155 is low is displayed on the display unit 155.

The signal processing/control unit 160 detects a change of theopen/closed state at step ST314, reads out the offset error correctiondata in accordance with the state after change at step ST306 or ST308 inaccordance with this, then displays the fact that the precision of theinformation of the bearing displayed on the display unit 155 is low onthe display unit 155 (ST320).

The signal processing/control unit 160 displays the information of thedrop of precision of the bearing on the display unit 155 by a methodsuch as making the image of a compass representing the bearing swingrightward and leftward, changing the shape, color, and size of thecompass, or displaying another image indicating a drop of the precisionof the bearing in the same way as step ST214 of FIG. 14.

The signal processing/control unit 160 displays information indicating adrop of precision of the bearing on the display unit 155 during theperiod of the correction of the earth-geomagnetism detection values(ST307/309) and the calculation of bearing (ST312). Then, whendisplaying the information of bearing after the correction on thedisplay unit 155, the signal processing/control unit 160 displays thefact that the precision of the bearing has been restored on the displayunit 155 (ST322). For example, when displaying a drop of precision ofthe bearing by movement swinging the image of a compass rightward andleftward, it may stop this rightward and leftward swinging. Whendisplaying the drop of precision of the bearing by changing the shape,color, and size of the image of the compass, it may return the image tothe original state. Alternatively, it is possible to display anotherimage indicating the restoration of the precision of the information ofthe bearing.

As described above, according to the example of the processing forcalculation of the bearing shown in FIG. 16, when the correction valuesof the earth-geomagnetism detection values change due to a change of theopen/closed state of the housings 2 and 3, during the period untilrecalculating the bearing by the new correction values and displayingthe results on the display unit 155, the fact that the precision of theinformation of the bearing being displayed is low can be notified to theuser. Due to this, the user becomes able to correctly grasp whether ornot the precision of the information of the bearing being displayed islow.

FIG. 17 is a flow chart illustrating an example of the processing forcalculation of the bearing in the cellular phone 100.

In the processing for calculation of the bearing of the example of FIG.15 and FIG. 16 explained above, a change of the earth-geomagnetismdetection values occurring due to an event such as the change of theopen/closed state of the housings 2 and 3 is corrected, but in a fifthexample explained next, a change of the earth-geomagnetism detectionvalues due to the occurrence of an event such as loading of a memorycard in the memory card unit 159 is corrected.

When the memory card uses parts which are easily magnetized such as thelead frame of a semiconductor integrated device, due to the influence ofthis magnetism, the offset error of the geomagnetic sensor 158 at thetime of the loading and nonloading of the memory card changes in certaincases.

FIG. 18 is a diagram showing an example of the change over time of thegeomagnetic sensor detection values (X-axis, Y-axis, Z-axis) inaccordance with loading of a memory card. In the example of FIG. 18, theX-axis, Y-axis, and Z-axis geomagnetic sensor detection values change byexactly “−7”, “−8”, and “−1”.

In the processing for calculation of the bearing of the example of FIG.17, in order to reduce the error of the bearing due to such changes ofthe geomagnetic sensor detection values, the correction values of theoffset error obtained by the processing for correction of offset errorare separately held for each of the events of the loading of the memorycard and the nonloading of the memory card. Then, when the loaded stateof the memory card of the case changes, the correction values used forthe correction of the offset error are changed matching with this.

When the start of the position finding processing is selected by the keyinput operation etc. at the key input unit 154, the signalprocessing/control unit 160 activates the geomagnetic sensor 158 andacquires the information of the bearing (ST402) and checks the loadedstate of the memory card in the memory card unit 159 (ST404). When it isjudged that the memory card is loaded by the signal from the memory cardunit 159, the signal processing/control unit 160 reads out the offseterror correction data of the time of the loading of the memory card heldin for example a not shown register in the signal processing/controlunit 160 (ST406) and corrects the detection values of the geomagneticsensor 158 based on this (ST407). Further, when it is judged that thememory card is not loaded by the signal by the signal from the memorycard unit 159, the signal processing/control unit 160 reads out theoffset error correction data of the time of the nonloading of the memorycard held in the not shown register in the signal processing/controlunit 160 (ST408) and corrects the detection values of the geomagneticsensor 158 based on this (ST409).

The offset error correction data of the time of the loading and the timeof the nonloading of the memory card is comprised of three correctionvalues corresponding to the magnetic detection values in the threedirections as shown in for example FIG. 18. These correction values arefrequently acquired at the time of the start of the position findingprocessing or the execution thereof by the processing for correction ofoffset error explained later and written into predetermined registers inthe signal processing/control unit 160 provided for each of the time ofloading and the time of nonloading of the memory card.

The offset error correction data stored in the register is rewrittenwhenever the processing for correction of offset error is executed andnew correction values are acquired.

When correcting the detection values of the geomagnetic sensor 158, thesignal processing/control unit 160 calculates the bearing by using theearth-geomagnetism detection values after this correction (ST412).

Then, the signal processing/control unit 160 confirms the loaded stateof the memory card in the memory card unit 159 again to check whether ornot the loaded state changes (ST414).

When detecting a change from a state where the memory card is not loadedin the memory card unit 159 to a state where the memory card is loadedin the memory card unit 159, the signal processing/control unit 160returns to step ST406 where it reads out the offset error correctiondata of the time of the loading of the memory card and repeats thecorrection of the earth-geomagnetism detection values and thecalculation of the bearing by using this (ST407, ST412). When detectinga change from a state where the memory card is loaded in the memory cardunit 159 to a state where the memory card is not loaded in the memorycard unit 159, the signal processing/control unit 160 returns to stepST408 where it reads out the offset error correction data of the time ofnonloading of the memory card and repeats the correction of theearth-geomagnetism detection values and the calculation of the bearingby using this (ST409, ST412).

When there is no change in the loaded state of the memory card, thesignal processing/control unit 160 confirms whether or not the end ofthe position finding processing is selected (ST416). When the positionfinding processing continues, it repeats the correction of theearth-geomagnetism detection values and the calculation of the bearingby using the offset error correction data in use at present (ST407/409,ST412).

When the end of the position finding processing is selected, the signalprocessing/control unit 160 stores the offset error correction data atthe time of the loading of the memory card and the time of thenonloading of the memory card held in the registers in the storage unit152 (ST418). Due to this, when the position finding processing iscarried out the next time, it becomes possible to smoothly perform thecalculation of the bearing by using the offset error correction datastored in the storage unit 152.

As described above, according to the example of the processing forcalculation of the bearing shown in FIG. 17, the change of the loadedstate of the memory card in the memory card unit 159 is monitored whenthe information of the bearing is displayed on the display unit 155, andwhen a change is detected, the information of the bearing displayed onthe display unit 155 is corrected in accordance with the state after thechange (loading or nonloading). Namely, when a change is detected in theloaded state of the memory card, the predetermined correctioncorresponding to the state after the change is carried out for thedetection values of the geomagnetic sensor 158, and the bearing iscalculated based on the earth-geomagnetism detection values after thiscorrection.

Accordingly, even when the detection values of the geomagnetic sensor158 change due to the change of the loaded state of the memory card, andthe precision of the information of the bearing displayed on the displayunit 155 is lowered, by detecting the change of the loaded state of thememory card in the memory card unit 155 and correcting the informationof the bearing, the precision of the information of the bearing can berestored.

Further, the offset error correction data in the loaded state and theunloaded state are separately held in predetermined registers of thesignal processing/control unit 160, and the correction of theinformation of the bearing is carried out by using the suitable offseterror correction data in accordance with the loaded state of the memorycard, therefore the information of the bearing can be corrected with ahigh precision in each state.

FIG. 19 is a flow chart illustrating an example of the processing forcalculation of the bearing in the cellular phone 100.

The difference of FIG. 19 from FIG. 17 explained above resides in thepoint during the period from the detection of the event of the change ofthe loaded state of the memory card to the recalculation of the bearingand the display of the recalculated information of the bearing on thedisplay unit 155, the fact that the precision of the information of thebearing displayed on the display unit 155 is low is displayed on thedisplay unit 155.

The signal processing/control unit 160 detects the change of the memorycard loaded state at step ST414 and reads out the offset errorcorrection data in accordance with the state after the change at stepST406 or ST408 in accordance with this, then makes the display unit 155display the fact that the precision of the information of the bearingdisplayed on the display unit 155 is low (ST420).

The signal processing/control unit 160 displays information indicatingsuch a drop of precision of the bearing on the display unit 155 duringthe period of the correction of the earth-geomagnetism detection values(ST407/ST409) and the calculation of bearing (ST412). Then, whendisplaying the information of the bearing after the correction on thedisplay unit 155, the signal processing/control unit 160 displays therestoration of the precision of the bearing on the display unit 155(ST422).

For example, when displaying a drop of the precision of the bearing bymovement swinging the image of the compass rightward and leftward, it ispossible to suspend this rightward and leftward swinging. Whendisplaying a drop of the precision of the bearing by changing the shape,color, and size of the image of compass, it is possible to return thisto the original state. Alternatively, it is possible to display anotherimage indicating the restoration of the precision of the information ofthe bearing.

As described above, according to the example of the processing forcalculation of the bearing shown in FIG. 19, when the correction valuesof the earth-geomagnetism detection values change due to a change of theloaded state of the memory card, during the period until recalculationof the bearing by the new correction values and display of the resultson the display unit 155, the fact that the precision of the bearingbeing displayed is low can be notified to the user. Due to this, theuser becomes able to correctly grasp whether or not the precision of theinformation of bearing being displayed is low.

Processing for Correction of Offset Error

The processing for correction of offset error is processing forcorrecting error of the constant earth-geomagnetism detection valuesoccurring due to a magnetic field generation source inside the cellularphone 100.

The static magnetic field generated inside the cellular phone 100 causesconstant error not dependent on the bearing in which the cellular phone100 is oriented in the detection values of the geomagnetic sensor 158.Contrary to this, the detection values of the earth-geomagnetism per sechange in accordance to the bearing in which the cellular phone 100 isoriented. Accordingly for example, by detecting the earth-geomagnetismwhile rotating the cellular phone 100 and finding the path of the vectorof the earth-geomagnetism in accordance with the rotation of thecellular phone 100, the offset error included in the detection values ofthe geomagnetic sensor 158 can be easily calculated.

The signal processing/control unit 160 displays an instruction on thedisplay unit 155 prompting the user to rotate the cellular phone 100when starting the position finding processing. When the user rotates thecellular phone 100 according to this instruction, the signalprocessing/control unit 160 acquires a plurality of detection values ofthe geomagnetic sensor 158 in the middle of the rotation, calculates theoffset error difference from the vector paths of the acquiredearth-geomagnetism detection values, and subtracts it from the detectionvalues of the geomagnetic sensor 158. Due to this, earth-geomagnetismdetection values in which the offset error is corrected are obtained.

The signal processing/control unit 160 stores the offset errorcalculated by the processing for correction of offset error as explainedabove as the offset error correction data in a predetermined register ofthe signal processing/control unit 160.

The signal processing/control unit 160 performs the above processing forcorrection of offset error for each constant time even during a periodwhere the position finding processing is executed.

The signal processing/control unit 160 performs the processing forcorrection of offset error and performs the correction of theearth-geomagnetism detection values even in the case where the detectionvalues of the geomagnetic sensor 158 become a predetermined abnormalstate such as overflow as will be explained next.

FIG. 20 is a flow chart illustrating an example of the processing forcorrection of offset error in the case where an event of the occurrenceof an abnormal state in the earth-geomagnetism detection values occurs.

When the start of the position finding processing is selected by the keyinput operation etc. at the key input unit 154 (ST502), the signalprocessing/control unit 160 checks whether or not the detection valuesof the geomagnetic sensor 158 have become a predetermined abnormal state(ST504).

Here, the “predetermined abnormal state” means for example the statewhere overflow occurs in any of the 8 bits of the detection valuesexpressed by whole number values of from “0” to “255” (that is any ofthe X-axis, Y-axis, and Z-axis earth-geomagnetism detection values) andthe values thereof become the maximum value “255” or the minimum value“0”. Further, where a normal range having an upper limit value and alower limit value is prescribed, any one of the earth-geomagnetismdetection values being out of this normal range may be defined as theabnormal state.

When detecting such a abnormal state of earth-geomagnetism detectionvalues, the signal processing/control unit 160 counts the time duringwhich the abnormal state continues from a point of time of the detection(ST506). Where the abnormal state continues for a predetermined time(for example 5 seconds), the signal processing/control unit 160 judgesthat the offset error occurs by magnetization etc. of the cellular phone100 and executes the above processing for correction of offset error(ST510).

After the processing for correction of offset error, the signalprocessing/control unit 160 checks whether or not the end of theposition finding processing is selected. When it confirms that theprocessing continues, it repeats the processing for steps St504 to ST510explained above (ST512).

Further, in a case where an abnormal state of the earth-geomagnetismdetection values is not detected at step ST504 or a case where it isjudged at step ST508 that the abnormal state of all detection values issolved within a predetermined time, it signal processing/control unit160 confirms the continuation of the position finding processing in thesame way, then repeats the processing for steps ST504 to ST510 (ST512).

As described above, according to the first example of the processing forcorrection of offset error shown in FIG. 20, in the case where thedetection values of the geomagnetic sensor 158 become a predeterminedabnormal state and this abnormal state continues for a predeterminedtime when displaying the information of the bearing on the display unit155, the correction of the information of the bearing is carried out.Namely, when any one (or a plurality of) detection values ofearth-geomagnetism in the three directions becomes a predeterminedabnormal state and this abnormal state continues for a predeterminedtime, the processing for detecting the offset error of the geomagneticsensor 158 and correcting this (processing for correction of offseterror) is carried out, and the bearing is re-calculated based on theearth-geomagnetism detection values after this correction. Accordingly,by monitoring for any abnormality of the detection values of thegeomagnetic sensor 158, the occurrence of the offset error of thecellular phone 100 is detected and suitable correction is carried out,therefore a drop of precision of the information of bearing due tooffset error can be suppressed.

Further, according to the processing of FIG. 20, the processing forcorrection of offset error is carried out when the earth-geomagnetismdetection values becomes a predetermined abnormal state continuouslyover a predetermined time. For this reason, cases where a temporaryabnormal state of earth-geomagnetism detection values occurring due tothe influence of external magnetic fields generated from for example abuilding or train is erroneously judged as offset error occurring due tothe magnetization etc. of the cellular phone 100 and the unsuitableprocessing for correction of offset error is executed can be reduced.

FIG. 21 is a diagram showing an example of the abnormal state of theearth-geomagnetism detection values occurring due to the influence ofthe external magnetic fields. In the example of the same diagram, theZ-axis direction earth-geomagnetism detection value is stuck at “0” overa time of 3 to 4 seconds. When the processing for correction of offseterror is executed when such a temporary abnormality due to the externalmagnetic fields occurs, the offset error cannot be correctly calculated,therefore the correction of the magnetic detection values is carried outwith the erroneous correction values, and the result of calculation ofthe bearing becomes incorrect as a result. The incorrect state of thebearing continues at least up to the next processing for correction ofthe offset error.

As shown in FIG. 21, the abnormal state of the earth-geomagnetismdetection values due to the influence of the external magnetic fields isusually transitional lasting just a few seconds and returns to thenormal state within for example 5 seconds in many cases.

Accordingly, as in the processing for FIG. 20, by distinguishing betweenan abnormal state occurring due to the influence of the externalmagnetic field and the offset error in accordance with whether or notthe abnormal state continues for the predetermined time or more andcontrolling the execution of the processing for correction of offseterror according to the result of this, the unsuitable execution of thecorrection processing can be effectively prevented.

FIG. 22 is a flow chart illustrating an example of the processing forcorrection of offset error in the cellular phone 100.

The difference of FIG. 22 from FIG. 20 explained above resides in apoint that the fact that the precision of the information of bearing islow is displayed on the display unit 155 during a period of correctionof the information of the bearing.

The signal processing/control unit 160 makes the display unit 155display the fact that the precision of the information of the bearingdisplayed on the display unit 155 is low after judging that anabnormality of the earth-geomagnetism detection values continues for apredetermined time or more at step ST508 (ST514).

The signal processing/control unit 160 displays the informationindicating such a drop of precision of the bearing on the display unit155 during the period of the processing for correction of offset error(ST510). Then, when displaying the information of the bearingrecalculated based on the earth-geomagnetism detection values after thecorrection on the display unit 155, the signal processing/control unit160 displays the restoration of the precision of the bearing on thedisplay unit 155 (ST516).

For example, when displaying a drop of the precision of the bearing bymovement swinging the image of the compass rightward and leftward, it ispossible to suspend this rightward and leftward swinging. Whendisplaying a drop of the precision of the bearing by changing the shape,color, and size of the image of compass, it is possible to return thisto the original state. Alternatively, it is possible to display anotherimage indicating the restoration of the precision of the information ofthe bearing.

As described above, according to the second example of the processingfor correction of offset error shown in FIG. 22, during the period ofthe correction of the information of the bearing along with anabnormality of the earth-geomagnetism detection values, the fact thatthe precision of the information of the bearing displayed on the displayunit 155 is low can be notified to the user. Due to this, the userbecomes able to correctly grasp whether or not the precision of theinformation of the bearing being displayed is low.

FIG. 23 is a flow chart illustrating an example of the processing forcorrection of offset error in the cellular phone 100.

The difference of FIG. 23 from FIG. 22 explained above resides in thatthe display of the map is fixed from the heading up display to the northup display during the period of the correction of information of theoverflow bearing explained above and the heading up display isre-started when the correction of the information of the bearing iscompleted.

When judging at step ST508 that an abnormality of the magnetic detectionvalues continues for a predetermined time or more, the signalprocessing/control unit 160 fixes the display of the map from theheading up display to the north up display (ST518). During the period ofthe processing for correction of offset error (ST510), it continues thenorth up display. Then, when the bearing is re-calculated based on theearth-geomagnetism detection values after this correction, the signalprocessing/control unit 160 releases the north up display and re-startsthe heading up display (ST520).

As described above, even in the example of the processing for correctionof offset error shown in FIG. 23, by fixing the display of the map tothe north up display during the period of correction of the informationof the bearing along with the occurrence of the event of the detectionof an abnormality of the earth-geomagnetism detection value, the factthat the precision of the information of the bearing displayed on thedisplay unit 155 is low can be notified to the user. Due to this, theuser becomes able to correctly grasp whether or not the precision of theinformation of the bearing being displayed is low.

Correction of error due to influence of external magnetic field

Next, the processing in the case where an error occurs in the detectionvalues of the geomagnetic sensor 158 due to the influence of theexternal magnetic field, and the precision of the information of thebearing is lowered will be explained.

In general, buildings, trains, etc. include many sources of generationof magnetic fields, therefore, in the insides and surroundings thereof,a big error occurs in the detection values of the geomagnetic sensor 158due to the influence of the external magnetic fields from these magneticfield generation sources. If the processing for correction of offseterror is executed in such an area, erroneous offset error is calculated,therefore, even after the user leaves this area, until he performs theprocessing for correction of offset error again, the information of theincorrect bearing is displayed on the display unit 155 as it is.

Therefore, in the processing explained below, when it is detected thatthe user has entered into an area where error occurs in the detectionvalues of the geomagnetic sensor 158 due to the influence of externalmagnetic fields etc., the processing for correction of offset error isprohibited. Further, the drop of the precision of the information of thebearing is displayed on the display unit 155, and the judgment ofwhether or not the user should use the information of the bearing as areference is enabled.

FIG. 24 is a flow chart illustrating an example of the processing in thecase where error occurs in the earth-geomagnetism detection values dueto the influence of external magnetic fields.

When the start of the position finding processing is selected by a keyinput operation etc. at the key input unit 154, the signalprocessing/control unit 160 activates the geomagnetic sensor 158 andacquires the information of the bearing (ST602) and checks whether ornot the level of the GPS signals received at the GPS signal receiver 151is lower than a predetermined value (ST604).

Usually, the level of the GPS signals becomes very small, even to a nonreceivable level, when the cellular phone 100 enters into a building. Inthe present example, by utilizing this nature, it is judged whether ornot the cellular phone 100 has entered into the inside of a building.

When it is detected that the GPS signals become lower than apredetermined value, the signal processing/control unit 160 judges thatthe cellular phone 100 has entered into the inside of a building andprohibits the execution of the processing for correction of offset errorexplained above (ST606). For example, in the case where the correctionprocessing is repeated each constant time, the correction processing isnot carried out even after this constant time passes. In this case, thesignal processing/control unit 160 makes the display unit 155 displaythe drop of the precision of the information of the bearing (ST608). Forexample, the signal processing/control unit 160 makes the display unit155 display the information of the drop of the precision of the bearingby for example the method of swinging the image of a compassrepresenting the bearing rightward and leftward, changing the shape,color, size etc. of the compass, or displaying another imagerepresenting the drop of precision of the bearing.

On the other hand, when it is detected that the GPS signals becomehigher than the predetermined value, the signal processing/control unit160 judges that the cellular phone 100 has not entered into the insideof the building and releases the prohibition if the state where theexecution of the processing for correction of offset error explainedabove is prohibited is exhibited (ST610). In this case, the signalprocessing/control unit 160 makes the display unit 155 display that theprecision of the information of the bearing is restored (ST612). Forexample, when displaying a drop of the precision of the bearing bymovement swinging the image of the compass rightward and leftward, it ispossible to suspend this rightward and leftward swinging. Whendisplaying a drop of the precision of the bearing by changing the shape,color, and size of the image of compass, it is possible to return thisto the original state. Alternatively, it is possible to display anotherimage indicating the restoration of the precision of the information ofthe bearing.

After step ST608 or ST612, the signal processing/control unit 160 checkswhether or not the end of the position finding processing is selected.When it confirms that the processing continues, the signalprocessing/control unit 160 repeats the above processing for step ST604and the following steps (ST614).

As described above, according to the example of the processing in thecase where error occurs in the earth-geomagnetism detection values dueto the influence of the external magnetic fields (FIG. 24), when theinformation of the bearing is displayed on the display unit 155, thelevel of the GPS signals received at the GPS signal receiver 151 ismonitored. When it is detected that this level becomes lower than apredetermined value, it is judged that the cellular phone 100 hasentered inside of a building, and information indicating that theprecision of the information of the bearing on the display unit 155 islow is displayed on the display unit 155. Due to this, the user becomesable to correctly grasp whether or not the precision of the informationof the bearing being displayed is low. For example, when the precisionof the information of the bearing is low, it becomes clear to the userthat the bearing must be predicted by another method, for example,comparing the information displayed on the map and the scene of thesurroundings to determine the bearing without reference to the bearingdisplayed on the screen, therefore the user friendliness of the mapinformation display processing function can be improved.

Further, the execution of the processing for correction of offset erroris prohibited in an unsuitable area where the offset error cannot becorrectly calculated due to the influence of external magnetic fields,for example, inside of a building, therefore the cases where the displayunit 155 displays the incorrect bearing for a long time can be reduced.

Next, an example of the processing in the case where error occurs in theearth-geomagnetism detection values due to the influence of an externalmagnetic field will be explained with reference to the flow chart shownin FIG. 25.

The difference of FIG. 25 from FIG. 24 explained above resides in thatthe display of the map is fixed from the heading up display to the northup display when it is detected that the GPS signals become lower than apredetermined value and the heading up display is re-started when it isdetected that the GPS signals become higher than the predeterminedvalue.

When it is detected that the GPS signals become lower than thepredetermined value at step ST604, the signal processing/control unit160 prohibits the processing for correction of offset error (ST606) and,at the same time, fixes the display of the map from the heading updisplay to the north up display (ST616). Further, when it detects thatthe GPS signals become higher than the predetermined value at stepST604, the signal processing/control unit 160 releases the prohibitionof the processing for correction of offset error (ST610) and, at thesame time, releases the north up display and re-starts the heading updisplay (ST618).

As described above, according to the processing of the example shown inFIG. 25, in an area where the precision of the information of thebearing is lowered due to the influence of an external magnetic fieldsuch as inside of a building, by fixing the display of the map to thenorth up display, the fact that the precision of the information of thebearing displayed on the display unit 155 is low can be notified to theuser. Due to this, the user becomes able to correctly grasp whether ornot the precision of the information of the bearing being displayed islow.

Next, an example of the processing in the case where error occurs in theearth-geomagnetism detection values due to the influence of an externalmagnetic field will be explained with reference to the flow chart shownin FIG. 26.

The difference of FIG. 26 from FIG. 25 explained above resides in thatwhen it is detected that the GPS signals become lower than apredetermined value, the processing for calculation of the bearing andthe operation of the geomagnetic sensor 158 are suspended, while when itis detected that the GPS signals become higher than a predeterminedvalue, these operations are restarted.

When it detects at step ST604 that the GPS signals become lower than thepredetermined value, the signal processing/control unit 160 fixes thedisplay of the map from the heading up display to the north up display(ST616) and, at the same time, suspends the processing for calculationof the bearing and the operation of the geomagnetic sensor 158 (ST620).When it detects at step ST604 that the GPS signals become higher than apredetermined value, the signal processing/control unit 160 releases thenorth up display and restarts the heading up display (ST618) and, at thesame time, restarts the processing for calculation of the bearing andthe operation of the geomagnetic sensor 158 (ST622).

The inside of a building etc. where it is originally hard to receive aGPS signal is also an environment easily influenced by external magneticfields, but according to the processing of the example of FIG. 26explained above, it is detected whether or not the cellular phone 100 isin such an environment in accordance with the level of the GPS signalsand when it is, the operation of the geomagnetic sensor 158 issuspended, therefore the supply of wasted electric power to circuitswhich are not utilized in the cellular phone 100 is suppressed, and areduction of the power consumption can be achieved.

Next, an example of the processing in the case where error occurs in theearth-geomagnetism detection values due to the influence of an externalmagnetic field will be explained with reference to the flow chart shownin FIG. 27.

The difference of FIG. 27 from FIG. 26 explained above resides in thatthe heading up display is restarted after the calculation value of thebearing is stabilized when it is detected that the GPS signals becomehigher than a predetermined value.

When detecting at step ST604 that the GPS signals become higher than thepredetermined value, the signal processing/control unit 160 restarts theprocessing for calculation of the bearing and the operation of thegeomagnetic sensor 158 (ST622), then judges whether or not thecalculation value of the bearing becomes stable (ST624). For example,the signal processing/control unit 160 judges that the calculation valueof the bearing is stabilized when the extent of change of the result ofcalculation of the bearing is within a predetermined range. Afterjudging that the calculation value of the bearing is stabilized, thesignal processing/control unit 160 releases the north up display andrestarts the heading up display (ST618).

As described above, according to the processing for the example shown inFIG. 27, when the signal level of the GPS signals becomes higher than apredetermined value and it is judged that the cellular phone 100 hasleft the inside of the building etc., the heading up display isrestarted after the stabilization of the calculation value of thebearing is confirmed. For this reason, the display of the information ofthe bearing having a low precision on the display unit 155 in forexample the state where the change of the earth-geomagnetism detectionvalues due to the magnetic fields from the building is large immediatelyafter the cellular phone leaves the building can be prevented.

Next, an example of the processing in the case where error occurs in theearth-geomagnetism detection values due to the influence of externalmagnetic fields will be explained with reference to the flow chart shownin FIG. 28.

In the processing for the example explained above (FIG. 24 to FIG. 27),based on the reception level of the GPS signals, it is judged whether ornot the cellular phone 100 has entered into a building, that is, whetheror not the cellular phone 100 has entered into an area where erroreasily occurs in the detection of the earth-geomagnetism due to theinfluence of external magnetic fields.

In the processing for the example (FIG. 28) explained next, based on theinformation previously registered in the storage unit 152, it is judgedwhether or not the present position of the cellular phone 100 isincluded in a precision drop area causing a drop of precision of thedetection values of the geomagnetic sensor 158. When it is judged thatthe present position is included in this area, the processing forcorrection of offset error is prohibited. Further, by making the displayunit 155 display the drop of the precision of the information of thebearing, the judgment of whether or not the user should use theinformation of the bearing as a reference is enabled.

When the start of the position finding processing is selected by a keyinput operation etc. at the key input unit 154, the signalprocessing/control unit 160 activates the geomagnetic sensor 158 andacquires the information of the bearing (ST702) and judges whether ornot the present position of the communication apparatus is included in aprecision drop area registered in the storage unit 152 (ST704).

The information of the precision drop area registered in the storageunit 152 is comprised of for example an identification number sent fromthe navigation server system 402 and information of the coordinates ofthe precision drop area on this map (for example, information indicatingthe precision drop area on the map by a range of coordinates).

The signal processing/control unit 160 first retrieves the informationof an identification number the same as the map being displayed atpresent from the information of the precision drop area registered inthe storage unit 152. When the result of retrieval is that informationof the same identification number exists, it is further judged whetheror not the present position of the cellular phone 100 is included in thecoordinate range of the precision drop area on the map indicated by thecoordinate information. When the present position is included in thiscoordinate range, the signal processing/control unit 160 judges that thepresent position of the cellular phone 100 is included in the precisiondrop area.

When it is judged that the present position is included in the precisiondrop area, the signal processing/control unit 160 prohibits theexecution of the above processing for correction of offset error(ST706). For example, when the correction processing is repeated eachconstant time, the correction processing is not carried out even afterthe elapse of this constant time. In this case, the signalprocessing/control unit 160 makes the display unit 155 display that theprecision of the information of the bearing has fallen (ST708). Forexample, the information of the drop of precision of the bearing isdisplayed on the display unit 155 by for example the method of swingingthe image of a compass representing the bearing rightward and leftward,changing the shape, color, size etc. of the compass, or displayinganother image representing the drop of precision of the bearing.

On the other hand, when it is judged that the present position existsoutside the precision drop area, the signal processing/control unit 160releases this prohibition so far as the state where the execution of theprocessing for correction of offset error is prohibited is exhibited(ST710). In this case, the signal processing/control unit 160 makes thedisplay unit 155 display that the precision of the information of thebearing is restored (ST712). For example, when displaying a drop of theprecision of the bearing by movement swinging the image of the compassrightward and leftward, it is possible to suspend this rightward andleftward swinging. When displaying a drop of the precision of thebearing by changing the shape, color, and size of the image of compass,it is possible to return this to the original state. Alternatively, itis possible to display another image indicating the restoration of theprecision of the information of the bearing.

After step ST708 or ST712, the signal processing/control unit 160 checkswhether or not the end of the position finding processing is selected.When it confirms that the processing continues, the signalprocessing/control unit 160 repeats the processing for step ST704 andthe following steps (ST714).

As described above, according to the example (FIG. 28) of the processingin the case where error occurs in the earth-geomagnetism detectionvalues due to the influence of an external magnetic field, whendisplaying the information of the bearing on the display unit 155, thejudgment of whether or not the present position of the cellular phone100 is included in the precision drop area registered in the storageunit 152 is carried out. When the result of this judgment is that it isjudged that the present position is included in the precision drop area,the information indicating that the precision of the information of thebearing on the display unit 155 is low is displayed on the display unit155. Due to this, the user becomes able to correctly grasp whether ornot the precision of the information of the bearing being displayed islow, therefore the user friendliness of the map information displayprocessing function can be improved.

Further, the execution of the processing for correction of offset erroris prohibited in the precision drop area where the offset error cannotbe correctly calculated due to the influence of an external magneticfield, therefore the case of displaying the incorrect bearing on thedisplay unit 155 over a long time can be reduced.

Next, a sixth example of the processing in the case where error occursin the earth-geomagnetism detection values due to the influence of anexternal magnetic field will be explained with reference to the flowchart shown in FIG. 29.

The difference of FIG. 29 from FIG. 28 explained above resides in thatthe display of map is fixed from the heading up display to the north updisplay when it is judged that the present position is included in theprecision drop area and the heading up display is restarted when it isjudged that the present position moves out of the precision drop area.

When judging that the present position of the cellular phone 100 isincluded in the precision drop area at step ST704, the signalprocessing/control unit 160 prohibits the processing for correction ofoffset error (ST706) and, at the same time, fixes the display of the mapfrom the heading up display to the north up display (ST716). When it isjudged at step ST704 that the present position moves out of theprecision drop area, the signal processing/control unit 160 releases theprohibition of the offset error correction value (ST710) and, at thesame time, releases the north up display and restarts the heading updisplay (ST718).

As described above, according to the processing for the example shown inFIG. 29, in an area where the precision of the information of thebearing is lowered due to the influence of an external magnetic field,by fixing the display of the map to the north up display, the fact thatthe precision of the information of the bearing displayed on the displayunit 155 is low can be notified to the user. Due to this, the userbecomes able to correctly grasp whether or not the precision of theinformation of the bearing being displayed is low.

Next, an example of the processing in the case where error occurs in theearth-geomagnetism detection values due to the influence of an externalmagnetic field will be explained with reference to the flow chart shownin FIG. 30.

The difference of FIG. 30 from FIG. 29 explained above resides in thatwhen it is judged that the cellular phone 100 enters a precision droparea based on the information of the storage unit 152, the processingfor calculation of the bearing and the operation of the geomagneticsensor 158 are suspended, while when it is judged that the cellularphone 100 moves out of the precision drop area, these operations arerestarted.

When judging at step ST704 that the present position of the cellularphone 100 is included in the precision drop area, the signalprocessing/control unit 160 fixes the display of the map from theheading up display to the north up display (ST716) and, at the sametime, suspends the processing for calculation of the bearing and theoperation of the geomagnetic sensor 158 (ST720). When it is judged atstep ST704 that the present position moves out of the precision droparea, the signal processing/control unit 160 releases the north updisplay and restarts the heading up display (ST718) and, at the sametime, restarts the calculation processing for the bearing and theoperation of the geomagnetic sensor 158 (ST722).

As described above, according to the processing for the example shown inFIG. 30, the operation of the geomagnetic sensor 158 is suspended in anarea where the precision of the information of the bearing is lowereddue to the influence of an external magnetic field, therefore the wastedsupply of electric power to the unused circuits is suppressed and areduction of the power consumption can be achieved.

Next, an example of the processing in the case where error occurs in theearth-geomagnetism detection values due to the influence of an externalmagnetic field will be explained with reference to the flow chart shownin FIG. 31.

The difference of FIG. 31 from FIG. 30 explained above resides in thatthe heading up display is restarted after the calculation value of thebearing is stabilized when it is judged that the cellular phone 100moves out of the precision drop area.

After judging at step ST704 that the present position of the cellularphone 100 is out of the precision drop area and restarting theprocessing for calculation of the bearing and the operation of thegeomagnetic sensor 158 (ST722), the signal processing/control unit 160judges whether or not the calculation value of the bearing is stabilized(ST724). For example, the signal processing/control unit 160 judges thatthe calculation value of the bearing is stabilized when the extent offluctuation in a predetermined time as the result of calculation of thebearing is contained within a predetermined range. Then, after judgingthat the calculation value of the bearing is stabilized, the signalprocessing/control unit 160 releases the north up display and restartsthe heading up display (ST718).

As described above, according to the processing for the example shown inFIG. 31, when it is judged that the present position of the cellularphone 100 is out of the precision drop area, after confirming that thecalculation value of the bearing is stabilized, the heading up displayis restarted. For this reason, immediately after the present positionmoves out of the precision drop area, when the fluctuation of theearth-geomagnetism detection values due to a magnetic field from thebuilding etc. remains, the low precision information of the bearing canbe prevented from being displayed on the display unit 155.

Next, the processing for registering a precision drop area in thestorage unit 152 in the processing for the example (FIG. 28 to FIG. 31)of correcting the influence of an external magnetic field explainedabove will be explained with reference to the flow chart of FIG. 32.

When the start of the position finding processing is selected by a keyinput operation etc. at the key input unit 154 (ST732), the signalprocessing/control unit 160 checks whether or not the detection valuesof the geomagnetic sensor 158 become a predetermined abnormal state(ST734).

Here, the “predetermined abnormal state” is the same as for example thatexplained in the processing for correction of offset error of FIG. 20.Namely, the state where overflow occurs in any one of the 8 bits ofdetection values expressed by whole number values of from “0” to “255”and the state where any one of the earth-geomagnetism detection valuesis out of the predetermined normal range are detected as abnormalstates.

When detecting such abnormal state of the earth-geomagnetism detectionvalues, the signal processing/control unit 160 counts the time duringwhich the abnormal state continues from the point of time of thedetection (ST736). Then, when the abnormal state ends within apredetermined time (for example 5 seconds), the signalprocessing/control unit 160 judges that error occurs in theearth-geomagnetism detection values due to an external magnetic field(ST738) and registers the present position as a precision drop area inthe storage unit 152 (ST740).

The precision drop area is registered in the storage unit 152 by storingthe identification number of the map displayed when detecting anabnormality of the earth-geomagnetism detection values and theinformation of the coordinates on the map where the abnormality occurs(for example the coordinate range of the a few meters square regionincluding the abnormality occurrence point) in correspondence in apredetermined precision drop area registration use data table assignedto the storage unit 152.

Note that an upper limit may be provided for the number of the precisiondrop areas registered in the storage unit 152. Xn this case, when thenumber of the precision drop areas registered in the storage unit 152reaches this upper limit, the signal processing/control unit 160 maydelete the oldest information from among the information of the alreadyregistered precision drop areas when registering a new precision droparea. Due to this, unlimited consumption of the storage region of thestorage unit 152 by the registered information of the precision dropareas can be prevented and, at the same time, by leaving the newestinformation, the reliability of the information of the precision dropareas can be raised.

After registering a precision drop area in the storage unit 152, thesignal processing/control unit 160 checks whether or not the end of theposition finding processing is selected (ST742). When it confirms thatthe processing continues, it repeats the processing for steps ST734 toST740 explained above.

Further, when the abnormal state of the earth-geomagnetism detectionvalues is not detected at step ST734 or when it is judged at step ST738that the abnormal state of the earth-geomagnetism detection valuescontinues over a predetermined time or more, the signalprocessing/control unit 160 confirms the continuation of the positionfinding processing in the same way, then repeats the processing forsteps ST734 to ST740.

Preferred embodiments of the present invention were explained above, butthe present invention is not limited to only the above aspects andincludes various variations.

In the above embodiments, an example of the processing for calculationof the bearing, an example of the processing for correction of offseterror, and an example of the processing in the case where error occurredin the earth-geomagnetism detection values due to the influence of anexternal magnetic field were shown, but the embodiments of the presentinvention include all combinations of any of these processing examples.

In the above embodiments, the example of the detection ofearth-geomagnetism in three directions in the geomagnetic sensor 158 wasshown, but the present invention is not limited to this. For example,two directions are also possible.

In the above embodiments, in for example step ST208 of FIG. 14, theexample of displaying a drop of the precision of the information of thebearing on the display unit 155 is shown, but the present invention isnot limited to this. For example, when correcting the information of thebearing when for example this display is carried out, the fact ofcorrection being in progress may be displayed on the display unit 155.Alternatively, information indicating both a drop of precision andcorrection in progress may be displayed on the display unit 155.

Further, the display of the information of the bearing may be simplystopped instead of displaying information such as the drop of precisionor correction in progress. In this case, when the correction of thebearing is completed (or when the phone leaves the precision drop area),the restoration of the precision of the information of the bearing maybe shown to the user by restarting the display of the information of thebearing.

At steps ST616 and ST618 of FIGS. 26 and 27, the fixing of the displayto the north up display and the release thereof are carried out, but thepresent invention is not limited to this. The display of a drop of theprecision of the bearing and the restoration of the precision of thebearing may be carried out in the same way as for example in steps ST608and ST612 of FIG. 24.

At steps ST716 and ST718 of FIGS. 30 and 31, the fixing of the displayto the north up display and the release thereof are carried out, but thepresent invention is not limited to this. The display of a drop of theprecision of bearing and the restoration of the precision of the bearingmay be carried out and in the same way as for example in steps ST708 andST712 of FIG. 28.

In the example of the processing where error occurs in theearth-geomagnetism detection value due to the influence of an externalmagnetic field (FIG. 28 to FIG. 31), the information of the precisiondrop area is acquired from the data table of the storage unit 152, butthe present invention is not limited to this. This information may beacquired from for example the server system connected via the wirelesscommunication unit 150. Namely, the signal processing/control unit 160acquires the information indicating whether or not the present positionof the cellular phone 100 is included in the precision drop area fromthe predetermined server system via the wireless communication unit 150and, where it is indicated in the acquired information that the presentposition is included in the precision drop area, may prohibit theprocessing for correction of offset error.

In the above embodiments, the processing for rotation of the map (forexample heading up display) is carried out in the cellular phone 100,but the present invention is not limited to this. For example, thecellular phone 100 may designate the orientation of the map with respectto the navigation server system 402 and request the map information, andthe navigation server system 402 may generate the map information in theorientation in response to the request from the cellular phone 100 andprovide the same to the cellular phone 100. Namely, the signalprocessing/control unit 160 may perform the processing for acquiring theimage information of the map in accordance with the bearing calculatedbased on the earth-geomagnetism detection values from the navigationserver system 402 and displaying the same on the display unit 155. Then,during this processing, when a drop of the detection precision of theearth-geomagnetism detection values is detected by for example the levelof the GPS signals becoming lower than a predetermined value, the signalprocessing/control unit 160 may request the image information of a mapof a previously set bearing to the navigation server system 402irrespective of the calculated bearing and acquire this and display thesame on the display unit 155.

In the above embodiments, the processing for calculation of the locationin accordance with the GPS signals is carried out in the GPS serversystem 401, but the present invention is not limited to this. Thecomputation for finding the location from the GPS signals may be carriedout in the cellular phone 100 as well.

In the above embodiments, the map information is acquired from thenavigation server system 402, but the present invention is not limitedto this. The map information may be stored in a storage device insidethe cellular phone 100 as well.

In the above embodiments, an example where the processing for the signalprocessing/control unit 160 is executed based on a program by a computeris shown, but it is also possible to execute at least part of theprocessing not according to the computer, but by hardware.

Conversely, the processing for at least part of the units other than thesignal processing/control unit 160 may be executed in the computer ofthe signal processing/control unit 160.

Further, the movable communication apparatus of the present invention isnot limited to a mobile phone. For example, the present invention can bewidely applied to communication devices which have communicationfunctions and are movable and preferably portable, for example PDAs(personal digital assistants).

1. A mobile communication terminal apparatus comprising: a geomagnetic sensor for detecting earth-geomagnetism; a displaying means; and a control means for calculating a geographical bearing base on values detected by the geomagnetic sensor, and displaying the resultant bearing information on the display means, and a position information acquisition means for acquiring information concerning a geographical position where the mobile communication terminal apparatus is positioned at this time, the control means displaying a map of the surrounding of a current position of the mobile communication terminal apparatus which is specified on the basis of the positional information acquired by the position information acquisition means, on the display means, displaying the bearing information included in the map on the display means, performing a control processing for controlling a direction of the map in a display screen of the display means in response to the calculated bearing, and stopping the control processing of the direction of the bearing when the detected value of the geomagnetic sensor becomes a predetermined abnormal state and the predetermined abnormal state lasts over a predetermined time, during the execution of the control processing, and then, fixing a predetermined bearing on the map to a predetermined direction on the display screen of the display means, and correcting the bearing information.
 2. A mobile communication terminal apparatus as set forth in claim 1, wherein the geomagnetic sensor detects a plurality of earth-geomagnetism in a plurality of perpendicular directions each other, the control means specifies an offset error of the geomagnetic sensor, when at least one of the detected values of the plurality of the earth-geomagnetism becomes the predetermined abnormal state and the predetermined abnormal state continues over a predetermined time, and corrects the bearing information by using the offset error.
 3. A mobile communication terminal apparatus as set forth in claim 1, wherein the predetermined abnormal state is a state where the detected value of the geomagnetic sensor is outside a range determined as normal.
 4. A mobile communication terminal apparatus as set forth in claim 1, wherein the geomagnetic sensor converts analog signals of the earth-geomagnetism to digital signals and outputs the same as the detected value of the earth-geomagnetism, and the predetermined abnormal state is a state where the detected value of the geomagnetic sensor is equal to a maximum value or a minimum value in the predetermined range.
 5. A mobile communication terminal apparatus as set forth in claim 1, wherein the control means restarts the control of the direction of the map, when the correction processing for the bearing information has completed, after stopped the control of the direction of the map.
 6. A correction method for correcting an error of a geomagnetic sensor for detecting earth-geomagnetism, used in a mobile communication terminal apparatus comprising a position information acquisition means for acquiring an information concerning a geographical position where the mobile communication terminal apparatus is positioned at this time, and a display means for displaying a geographical bearing information calculated on the basis of the detected value of the geomagnetic sensor, the correction method including; a first step for displaying a map of the surrounding of a current position of the mobile communication terminal apparatus which is specified on the basis of the positional information acquired by the position information acquisition means, on the display means, a second step for displaying the bearing information included in the map on the display means, a third step for performing a control processing for controlling a direction of the map in a display screen of the display means in response to the calculated bearing, and stopping the control processing of the direction of the bearing when the detected value of the geomagnetic sensor becomes a predetermined abnormal state and the predetermined abnormal state lasts over a predetermined time, during the execution of the control processing, and then, fixing a predetermined bearing on the map to a predetermined direction on the display screen of the display means, and correcting the bearing information, a fourth step for detecting the fact that the detected value of the geomagnetic sensor becomes a predetermined abnormal state under the status where the control of the direction of the map in the third step, a fifth step for monitoring whether or not the predetermined abnormal state being continued over a predetermined time, after the detection of the predetermined abnormal state, a sixth step for stopping the control of the direction of the map in the third step and correcting the bearing information, when the predetermined abnormal state has continued over a predetermined time, and a seventh step for displaying a predetermined bearing on the map on the displaying means in a condition where the predetermined bearing is fixed to a predetermined direction on the display screen of the display means.
 7. A correction method as set forth in claim 6, further including: an eighth step for detecting a plurality of earth-geomagnetism in a plurality of perpendicular directions each other, by the geomagnetic sensor, and a ninth step for specifying an offset error of the geomagnetic sensor, when at least one of the detected values of the plurality of the earth-geomagnetism becomes the predetermined abnormal state and the predetermined abnormal state continues over a predetermined time, and corrects the bearing information by using the offset error.
 8. A correction method as set forth in claim 6, wherein the predetermined abnormal state is a state where the detected value of the geomagnetic sensor is outside a range determined as normal.
 9. A correction method as set forth in claim 6, further including a tenth step for converting analog signals of the earth-geomagnetism to digital signals and outputs the same as the detected value of the earth-geomagnetism, and wherein the predetermined abnormal state is a state where the detected value of the geomagnetic sensor is equal to a maximum value or a minimum value in the predetermined range.
 10. A correction method as set forth in claim 6, further including an eleventh step for restarting the control of the direction of the map, when the correction processing for the bearing information has completed, after stopped the control of the direction of the map. 